About two-thirds of Americans object to online tracking by advertisers--and that number rises once they learn the different ways marketers are following their online movements, according to a new survey from professors at the University of Pennsylvania and the University of California, Berkeley.

The professors say they believe the study, scheduled for release on Wednesday, is the first independent, nationally representative telephone survey on behavioral advertising.

The topic may be technical, but it has become a hot political issue. Privacy advocates are telling Congress and the Federal Trade Commission that tracking of online activities by Web sites and advertisers has gone too far, and the lawmakers seem to be listening. Representative Rick Boucher, Democrat of Virginia, wrote in an article for The Hill last week that he planned to introduce privacy legislation. And David Vladeck, head of consumer protection for the FTC, has signaled that he will examine data privacy issues closely.

Marketers are arguing that advertising supports free online content. Major advertising trade groups proposed in Julysome measures that they hoped would fend off regulation, like a clear notice to consumers when they were being tracked.

The data in this area, however, has been largely limited to company-financed research or Internet-based research, which survey experts say they believe is not representative of all Americans. So the study--among the first independent surveys to examine this issue--has attracted widespread interest.

"This research is going to ignite an intense debate on both sides of the Atlantic on what the appropriate policy should be," said Jeffrey Chester, executive director of the privacy group Center for Digital Democracy, which did not work on the study.

The study's authors hired a survey company to conduct interviews with 1,000 adult Internet users. The interview, which lasted about 20 minutes, included questions like "Please tell me whether or not you want the Web sites you visit to give you discounts that are tailored to your interests." The results were later adjusted to reflect Census Bureau patterns in categories like sex, age, population density and telephone usage.

Tailored ads in general did not appeal to 66 percent of respondents. Then the respondents were told about different ways companies tailor ads: by following what someone does on the company's site, on other sites and in offline places like stores.

The respondents' aversion to tailored ads increased once they learned about targeting methods. In addition to the original 66 percent that said tailored ads were "not OK," an additional 7 percent said such ads were not OK when they were tracked on the site. An additional 18 percent said it was not OK when they were tracked via other Web sites, and an additional 20 percent said it was not OK when they were tracked offline.

The survey company also asked about customized discounts and customized news. Fifty-one percent of respondents said that tailored discounts were OK, and 58 percent said that customized news was fine.

On the advertising question, there was not a big difference between age groups. Marketers often use teenagers' behavior on Facebook as anecdotal evidence that they do not mind handing over information. But 55 percent of respondents from 18 to 24 objected to tailored advertising.

"We sometimes think that the younger adults in the United States don't care about this stuff, and I would suggest that's an exaggeration," said Joseph Turow, lead author of the study and a professor of communication at the Annenberg School for Communication at the University of Pennsylvania. His co-authors are professors at Berkeley's law school and at the Annenberg Public Policy Center at the University of Pennsylvania.

The survey also asked nine true-or-false questions about privacy laws to see how knowledgeable Americans were about protection, including "If a Web site has a privacy policy, it means that the site cannot share information about you with other companies, unless you give the Web site your permission." (The correct answer is "false.") On only one question, regarding sweepstakes, was answered correctly by more than half of respondents.

Finally, the survey sought opinions on laws regarding tracking, asking if there should be a law that gave people the right to know everything a Web site knew about them. Sixty-nine percent of respondents said yes. Respondents also overwhelmingly supported a hypothetical law that required Web sites and advertising companies to delete all information about an individual upon request; 92 percent endorsed it.

"I don't think that behavioral targeting is something that we should eliminate, but I do think that we're at a cusp of a new era, and the kinds of information that companies share and have today is nothing like we'll see 10 years from now," Turow said. He said he would like "a regime in which people feel they have control over the data that marketers collect about them. The most important thing is to bring the public into the picture, which is not going on right now."

Stuart P. Ingis, a partner at the law firm Venable who represents the industry trade groups' self-regulation coalition, said that the industry was taking steps to explain to consumers how behavioral targeting worked.

"The more people understand the practices and how the data is actually being used, that's when the concerns disappear," he said. Just because many Americans are not in favor of something does not mean it should be banned, he said, citing negative feelings about taxes.

But Chester, whose group is part of a privacy coalition calling for congressional action, said the survey would be helpful. "This research gives the FTC and Congress a political green light to go ahead and enact effective, but reasonable, rules and policies," he said.